Fix replace_text*() functions

* Now return an error code
* Completely rewrote replace_text()

2 files changed, 78 insertions, 32 deletions

diff --git a/include/relocation.h b/include/relocation.h
index ea9da9f..b734433 100644
--- a/include/relocation.h
+++ b/include/relocation.h
@@ -16,7 +16,7 @@
 #endif
 #include <unistd.h>
 
-void replace_text(char *original, const char *target, const char *replacement);
-void file_replace_text(const char* filename, const char* target, const char* replacement);
+int replace_text(char *original, const char *target, const char *replacement);
+int file_replace_text(const char* filename, const char* target, const char* replacement);
 
 #endif //OMC_RELOCATION_H
diff --git a/src/relocation.c b/src/relocation.c
index b92af2b..8b18efd 100644
--- a/src/relocation.c
+++ b/src/relocation.c
@@ -10,7 +10,10 @@
  * ~~~{.c}
  * char *str = (char *)calloc(100, sizeof(char));
  * strcpy(str, "This are a test.");
- * replace_text(str, "are", "is");
+ * if (replace_text(str, "are", "is")) {
+ *     fprintf(stderr, "string replacement failed\n");
+ *     exit(1);
+ * }
  * // str is: "This is a test."
  * free(str);
  * ~~~
@@ -18,64 +21,106 @@
  * @param original string to modify
  * @param target string value to replace
  * @param replacement string value
+ * @return 0 on success, -1 on error
  */
-void replace_text(char *original, const char *target, const char *replacement) {
+int replace_text(char *original, const char *target, const char *replacement) {
     char buffer[OMC_BUFSIZ];
-    char *tmp = original;
+    char *pos = original;
+    char *match = NULL;
+    size_t original_len = strlen(original);
+    size_t target_len = strlen(target);
+    size_t rep_len = strlen(replacement);
+    size_t buffer_len = 0;
+
+    if (original_len > sizeof(buffer)) {
+        errno = EINVAL;
+        SYSERROR("The original string is larger than buffer: %zu > %zu\n", original_len, sizeof(buffer));
+        return -1;
+    }
 
     memset(buffer, 0, sizeof(buffer));
-    while (*tmp != '\0') {
-        if (!strncmp(tmp, target, strlen(target))) {
-            size_t replen;
-            char *stop_at = strchr(tmp, '\n');
-            if (stop_at) {
-                replen = (stop_at - tmp);
-            } else {
-                replen = strlen(replacement);
+    if ((match = strstr(pos, target))) {
+        while (*pos != '\0') {
+            // append to buffer the bytes leading up to the match
+            strncat(buffer, pos, match - pos);
+            // position in the string jump ahead to the beginning of the match
+            pos = match;
+
+            // replacement is shorter than the target
+            if (rep_len < target_len) {
+                // shrink the string
+                strcat(buffer, replacement);
+                memmove(pos, pos + target_len, strlen(pos) - target_len);
+                memset(pos + (strlen(pos) - target_len), 0, target_len);
+            } else { // replacement is longer than the target
+                // write the replacement value to the buffer
+                strcat(buffer, replacement);
+                // target consumed. jump to the end of the substring.
+                pos += target_len;
+            }
+            // find more matches
+            if (!(match = strstr(pos, target))) {
+                // no more matches
+                // append whatever remains to the buffer
+                strcat(buffer, pos);
+                // stop
+                break;
             }
-            strcat(buffer, replacement);
-            strcat(buffer, "\n");
-            tmp += replen;
-        } else {
-            strncat(buffer, tmp, 1);
         }
-        tmp++;
     }
+
+    buffer_len = strlen(buffer);
+    if (buffer_len < original_len) {
+        // truncate whatever remains of the original buffer
+        memset(original + buffer_len, 0, original_len - buffer_len);
+    }
+    // replace original with contents of buffer
     strcpy(original, buffer);
+    return 0;
 }
 
 /**
  * Replace `target` with `replacement` in `filename`
  *
  * ~~~{.c}
- * file_replace_text("/path/to/file.txt, "are", "is");
+ * if (file_replace_text("/path/to/file.txt, "are", "is")) {
+ *     fprintf(stderr, "failed to replace strings in file\n");
+ *     exit(1);
+ * }
  * ~~~
  *
  * @param filename path to file
  * @param target string value to replace
  * @param replacement string
+ * @return 0 on success, -1 on error
  */
-void file_replace_text(const char* filename, const char* target, const char* replacement) {
-    FILE *fp = fopen(filename, "r");
-    if (fp == NULL) {
-        fprintf(stderr, "unable to open for reading: %s\n", filename);
-        return;
-    }
-
+int file_replace_text(const char* filename, const char* target, const char* replacement) {
+    int result;
     char buffer[OMC_BUFSIZ];
     char tempfilename[] = "tempfileXXXXXX";
-    FILE *tfp = fopen(tempfilename, "w");
+    FILE *fp;
+    FILE *tfp;
+
+    fp = fopen(filename, "r");
+    if (!fp) {
+        fprintf(stderr, "unable to open for reading: %s\n", filename);
+        return -1;
+    }
 
-    if (tfp == NULL) {
-        fprintf(stderr, "unable to open temporary fp for writing: %s\n", tempfilename);
+    tfp = fopen(tempfilename, "w");
+    if (!tfp) {
+        SYSERROR("unable to open temporary fp for writing: %s", tempfilename);
         fclose(fp);
-        return;
+        return -1;
     }
 
     // Write modified strings to temporary file
+    result = 0;
     while (fgets(buffer, sizeof(buffer), fp)) {
         if (strstr(buffer, target)) {
-            replace_text(buffer, target, replacement);
+            if (replace_text(buffer, target, replacement)) {
+                result = -1;
+            }
         }
         fputs(buffer, tfp);
     }
@@ -86,4 +131,5 @@ void file_replace_text(const char* filename, const char* target, const char* rep
     // Replace original with modified copy
     remove(filename);
     rename(tempfilename, filename);
+    return result;
 }
\ No newline at end of file